It is well known in the industry to record digital information on optical disks. One problem associated with such recording is that of unauthorized copies. A typical optical disk may include a bar code provided near the mounting hole of the optical disk and an area on the disk in which a digital information is recorded. The bar code uniquely identifies the optical disk. A problem with this arrangement is that of unauthorized copies. As industry progresses new disks are being proposed such as the digital video disk (DVD) which could include multiple surfaces for recording information such as movies, games, audio, text, and software. Although copyright protection is available it in and of itself, does not prevent unauthorized copies. A scrambling technique is available, however, they are costly and time consuming and they prohibit copying when it may be desired to have a single copy made.
A CD-ROM or the like is manufactured according to the published standards such as ISO 9660 standards established by International Standard Organization. To prevent illegally copying of information from a legitimate optical disk in conformity with the standards, a copy protection code is preliminarily recorded on the optical disk. Thus, an optical disk containing such a copy protection code is judged to be legitimate. On the other hand, an optical disk lacking a copy protection code is judged to be illegal. The effect of such a copy protection method is limited for the following reason. When all information on a legitimate optical disk is copied and transferred to another optical disk (a second optical disk), the second optical disk can also be used as a legitimate optical disk.
Another solution for disk copy protection is to use a hardware key or a special data disk referred to as a key disk for the protection. However, this method requires additional medium for carrying the key in the form of hardware or separate disk which increase the cost and gives users a potential problem that the recording medium is impossible to be used when breakage of the hardware key, the key disk or missing of the key disk occurs.
Another solution, presented in U.S. Pat. No. 5,572,589, is to serialize disks by physically damaging a portion of the disc to create a pattern of damage. The pattern of damage is encoded in an identifying value and the disc is marked with the identifying value to distinguish the disc from other discs. The disadvantage of this method is that it requires scarifying the disk capacity by damaging useful recording area.
Presently, there are many activities in standardization of new generation of optical disk, called digital video disks (DVD). The situation now is different from one when compact disk (CD) standards were to be accepted, since in near future the variety of media will appear that will allow an ordinary user, with a personal computer (PC), and a general purpose software, to record his own disks. So, the DVD drive must contain more sophisticated copy protection mechanisms compared to CD drive.
One way to protect data of being copied on another disk is to record the copy protection code on a separate area on a disk where optical head cannot scan it and to use this code as a key to encrypt the user data before recording.
U.S. Pat. No. 5,274,623 discloses an optical disk defining a central mounting opening and having top and bottom surfaces, wherein information is recorded in a recording area which is read from the top surface of the disk. Encryption key is recorded on the outer peripheral edge of the optical disk in the form of a serrated pattern perpendicular to the surface of recording layer. The problem with this arrangement is that it is difficult to form the serrated pattern defining the encryption key on the outer peripheral edge during manufacture and also to provide the necessary space to read such key by either a writer or a reader.
Commonly Assigned U.S. Pat. No. 5,430,281 discloses an optical disk media having an identification code embedded therein called the bar code. However the bar code is not used for the encrypting the data to be recorded to the disk and decrypting the data read out from the disk.
Commonly Assigned U.S. Pat. No. 5,489,768 discloses an optical disk with bar codes, wherein the bar codes are used to prevent inappropriate files from being stored on the medium by preventing an unauthorized system attempting to interact with the storage medium. Although bar codes disclosed in this patent are not used for the encryption of the data to be recorded on the disk, they obviously can be used in this purpose.